With the development of technologies, electronic lighting devices (e.g., LED lamps) that utilize equivalent electric load have gradually replaced traditional incandescent lamps, and thus becoming illumination sources in people's daily life.
Currently, LED dimmers are utilized to adjust the current or voltage of the power supply, so that as the load, a LED lamp can output lights with different brightness. Specifically, there are two main types of LED dimmers: silicon controlled rectifier based leading-edge phase cut dimmer (also called forward-phase control dimmer, or FPC dimmer) and transistor-based trailing-edge phase cut dimmer (also called reverse-phase control dimmer, or RPC dimmer).
FIG. 1 illustrates a wave-function diagram of a leading-edge phase cut AC sinusoidal voltage. As shown in FIG. 1, the leading-edge phase cut dimmer (SCR-based) utilizes the properties of a silicon controlled rectifier (SCR) to perform phase cutting from the start of each AC power source half-cycle, and after a certain period of time corresponding to the dimming positions, the circuit starts conducting to supply power to the load till the end of the half cycle. After passing the zero-crossing point, the same operation is repeated, thus changing the effective value of the AC current. That is, when the leading-edge phase cut dimmer (SCR-based) performs phase cutting, namely, starting from the zero-crossing point in the AC phase, the input voltage is chopped, and until when the SCR device is conducting, the voltage input recovers. Specifically, when the leading-edge phase cut dimmer (SCR-based) is triggered, a certain period of time is required to load the current to keep the dimmer conducting. This current is called a holding current, and if the holding current is removed or weakened, the leading-edge phase cut dimmer (SCR-based) is then turned off.
FIG. 2 illustrates a wave-function diagram of a trailing-edge phase cut AC sinusoidal voltage. As shown in FIG. 2, when the AC phase is zero, the trailing-edge phase cut dimmer (transistor-based) is triggered and starts conducting, and after a period of time corresponding to the dimming positions, the dimmer is turned off to realize phase cutting. The trailing-edge phase cut dimmer (transistor-based) controls the switch-on and switch-off of the field effect transistor via a timing circuit. Specifically, the switch is switched on from the start of each AC power source half-cycle, and after a certain period of time corresponding to the dimming positions, the switch is switched off till the end of the half cycle. After passing the zero-crossing point, the same operation is repeated, thus changing the effective value of the AC current.
However, when using the leading-edge phase cut dimmer (SCR-based) to modulate the LED lights, components like capacitors are needed in the dimming circuit to provide a holding current that keeps the leading-edge phase cut dimmer (SCR-based) conducting. If there is no dimmer in the dimming circuit or a trailing-edge phase cut dimmer (transistor-based) is used in the dimming circuit, the waveform outputted by the dimming circuit may be influenced due to charging/discharging processes of the components like capacitors. Accordingly, the phenomenon of LED lamp flicker occurs.
The disclosed dimmer control circuit, dimmer control method, and lighting device are directed to solve one or more problems set forth above and other problems.